A nanocomposite coating was formed by incorporating nanoalumina pigment in a waterborne polyurethane dispersion (WPUD) to different loading levels (0.1% and 1.0% by weight). Electrochemical performance of the nanocomposite coating was evaluated by applying these nanomodified coatings on mild steel substrate and exposing them to salt-spray, humidity, and accelerated UV weathering. The surface morphology of the composite coating was evaluated using various analytical techniques. SEM and AFM were used to investigate the dispersion of nanoalumina pigment and surface morphological changes of the nanomodified coating, before and after exposure to the test environment. Mechanical properties like scratch resistance were studied by using nanoscratch technique (Nanoindenter TI-900, Hysitron Inc, USA) and hardness using pencil hardness test method. The results showed an improvement in the corrosion, UV weathering, and mechanical properties of the coatings at lower concentration (0.1% by wt), indicating the positive effect of addition of nanoalumina pigment to the coating. 1. Introduction An aqueous polyurethane dispersion is a binary colloid system in which polyurethane particles are dispersed in a continuous aqueous medium [1, 2]. The basic building blocks of solvent borne polyurethanes like diisocyanates, polyols, amines catalysts, and additives are common to aqueous-based system as well [3]. Though, the development of aqueous polyurethane dispersions was motivated primarily by environmental considerations, one technical advantage of aqueous polyurethane dispersion is that the viscosity of dispersion is independent of the molecular weight of polymer. Thus, polyurethane dispersion can be prepared at a high solid content with a molecular weight high enough to form films with excellent performance solely by physical drying [2]. Economical aspect is another reason as they do not contain the expensive solvents [3]. Compared to their solvent counterparts, polyurethane dispersions can offer the following advantages: viscosity and flow properties independent of molecular weight, the absence of external emulsifiers, environmental safety, good adhesion, and rheology characteristics [4]. Other advantages which make them attractive as waterborne coatings are the outstanding properties of solvent, stain, chemical resistance, and toughness with flexibility [5]. Also, it has been found that additive and pigments not only provides esthetics to the waterborne coatings, but also helps in improving many properties of the coatings such as UV resistance, corrosion resistance. With
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